Over the past few years, progress in higher recording densities for magnetic disk devices has been remarkable. Accompanying this progress is the development of narrower magnetic poles which are included in magnetic recording heads, which has been striking. However, a problem is that the requisite recording magnetic field strength becomes difficult to achieve as the magnetic pole becomes narrower because the recording magnetic field strength generated by a magnetic recording head is correlated to the volume of the magnetic pole.
One solution to this problem is a thermally assisted magnetic recording method. Thermally assisted recording lowers the magnetic field strength required to write by heating the magnetic recording medium and lowering the coercive force while recording. Recently, microwave-assisted recording has been proposed as another assisted recording method for achieving recording densities of at least 1 Tb/in2. For example, microwave-assisted recording methods which employ spin torque oscillation are proposed in WIPO Pub. No. WO03/010758A1; Digest of the 18th Magnetic Recording Conference: Heads and Systems, TMRC-2007-B7, May 21-23 (2007); and Jian-Gang Zhu, Xiaochun Zhu, and Yuhui Tang, IEEE Transactions Magnetics, Vol. 44, No. 1, pp. 125-131 (2008). In this method, a magnetized high-speed rotor in which magnetization is rotated at high speed by the spin torque is arranged adjacent to the main magnetic pole of a vertical magnetic recording head, microwaves irradiate a magnetic recording medium, and information is recorded on the magnetic recording medium which has large magnetic anisotropy. The magnetic field required for magnetization reversal of the medium is reduced by applying microwaves generated by an oscillator to the medium. The required recording magnetic field strength which is generated by the main magnetic pole of the magnetic recording head exhibits a lower strength than previous heads.
In microwave-assisted recording, strong microwaves can irradiate a region on the order of nanometers of a magnetic recording medium, locally establish a magnetic resonance state, and reduce the magnetic field for magnetization reversal to record information. Since both the microwaves and the magnetic field from the main magnetic pole are used to record magnetized bits, a microwave (high-frequency magnetic field) generator may be positioned in the vicinity of the main magnetic pole and may be affected by a large magnetic field from the main magnetic pole. When the microwave generator is affected by a large magnetic field, there are problems from the perspectives of performance and reliability such as the magnetization of the magnetic body in the microwave generator being oriented in one direction, and the magnetization not rotating efficiently.
In light of the above situation, it would be beneficial to the art of microwave assisted magnetic recording to provide a magnetic recording head which overcomes the problems associated with conventional microwave assisted designs.